Synthetic materials for prostheses and similar applications are in demand. In one application, it is known that, as adults age, the accommodative power of the eye decreases leading to the onset of presbyopia. This age-related decrease in accommodative power is believed to be caused by a decrease in the elasticity of the lens material. This decrease is probably caused by denaturation and dehydration of the lens material. Thus the loss of accommodation results from a change in elasticity rather than a decrease in the action of the ciliary muscles. The replacement of the original lens with a synthetic polymer having the elasticity equivalent to the lens of a young adult offers the prospect of being able to use a surgical procedure to replace the need for glasses to correct presbyopia.
The use of polymeric prostheses and biomedical mouldings has grown rapidly in recent times. Such mouldings may be used for contact lenses or for specific ophthalmic purposes. For example, they may be used for intraocular lenses and eye bandages. They may also be used for surgical mouldings such as heart valves and artificial arteries. Other applications include wound dressings, biomedical adhesives and tissue scaffolds. Use in drug delivery is a further application.
Diseases of the lens material of the eye are often in the form of cataracts. The ideal cataract procedure is considered to be one where the lens capsule bag is maintained with the cataractous lens material removed through a small opening in the capsule. The residual epithelial cells of the lens are removed chemically and/or with ultrasound or lasers followed by aspiration. A biocompatible artificial lens (also called an “IOL”, such as known PMMA lenses) with appropriate optical clarity, refractive index and mechanical properties is then inserted into the capsular bag to restore the qualities of the original crystalline lens. The desired refractive index is about 1.41. For many years most of these lenses have been made of poly(methylmethacrylate) (PMMA), a material with good optical characteristics and compatibility with tissues in the eye. However, PMMA is a very rigid material (and therefore non-accommodating) and the incision must be made big enough, at least 5-6 mm, for implantation of the lens. With improved devices for removal of the natural lens that require only small (3-4 mm) incision, there is a need for lenses which are foldable.
There have also been recent advances in methods of inserting intraocular lens. For example, U.S. Pat. No. 5,772,667 assigned to Pharmacia Lovision Inc., discloses an intraocular lens injector. This device compresses an IOL by rolling the lens into a tight spiral. The device then injects the compressed IOL through a relatively small incision in the eye, approximately 2-3 millimeters in length, resulting from a phacoemulsification procedure. The IOL is inserted into a receiving channel of the injector device in an uncompressed state and is urged into a cylindrical passageway. As the IOL advances into the cylindrical passageway, the IOL rolls upon itself into a tightly rolled spiral within the confines of the cylindrical passageway. An insertion rod is then inserted into an open end of the cylindrical passageway and advances the compressed IOL down the passageway. As the IOL exits the passageway and enters the eye, the IOL will expand back to its uncompressed state. Although these IOLs offer significant advances the implantation of these types of non-accommodating IOLs still requires the patient to use spectacle correction for reading.
To avoid the need for such injection devices and to also overcome the limitation of conventional IOLs (namely, requiring reading spectacles), it has been proposed that intraocular lenses be formed in situ after being injected as a liquid flowable form into the lens capsule bag. However, while this concept is attractive in that smaller incisions would be required, it raises further difficulties in that further chemical reactions are required to cure the injectable material and these are required to be not harmful to the patient. It is also a requirement that the chemical reactions can take place over a relatively short time under mild reaction conditions. It is desirable that the reaction is also not significantly inhibited by oxygen. A still further requirement is that no by-products or residues are produced that may have an adverse biological effect on the patient.
In our co-pending international patent application PCT/AU00/00915 references relating to ethylenically unsaturated macromonomers are discussed and an invention relating to novel macromonomers suitable for use as injectable precursors for intraocular lenses are described. In particular, there is described an ethylenically unsaturated macromonomer comprising units of formula:
where L is a linker group
Z is an ethylenically unsaturated free radical polymerisable group
y is ≧2
x is ≧5
and wherein the ethylenically unsaturated groups are provided by (meth)acrylate or (meth)acrylamide moieties. The linker group, L, functions as a spacing group which allows the required ethylenic unsaturated group Z to be attached to the copolymer backbone. It may be a linear, branched or cyclic hydrocarbyl chain. It may contain hetero atoms as well as carbonyl and other substituted atoms. The entire contents of that specification (published as WO 01/08603) is incorporated herein by reference.
Although the macromonomers described in that specification meet many of the requirements for the preferred end use application we have now found a new class of macromonomer that provides accommodating intraocular lenses with superior properties.